First Observation of the decay KL -> pi0 e e gamma

TL;DR

This paper reports the first observation of the decay KL -> pi0 ee gamma, measuring its branching ratio and confirming theoretical predictions from chiral perturbation theory including vector meson contributions.

Contribution

First experimental observation of the decay KL -> pi0 ee gamma with measured branching ratio and validation of chiral perturbation theory calculations.

Findings

Branching ratio measured as (2.34 +/- 0.35 +/- 0.13)x10^{-8}

Parameter a_V fitted as -0.67 +/- 0.21 +/- 0.12

Results consistent with theoretical predictions and previous measurements.

Abstract

We report on the first observation of the decay KL -> pi0 ee gamma by the KTeV E799 experiment at Fermilab. Based upon a sample of 48 events with an estimated background of 3.6 +/- 1.1 events, we measure the KL -> pi0 ee gamma branching ratio to be (2.34 +/- 0.35 +/- 0.13)x10^{-8}. Our data agree with recent O(p^6) calculations in chiral perturbation theory that include contributions from vector meson exchange through the parameter a_V. A fit was made to the KL -> pi0 ee gamma data for a_V with the result -0.67 +/- 0.21 +/- 0.12, which is consistent with previous results from KTeV.